Fluorescence polarization instruments and their use for clinical applications are described for instance in, "Design, Construction, and Two Applications for an Automated Flow-Cell Polarization Fluorometer with Digital Read Out: etc."; R. D. Spencer, F. D. Toledo, B. T. Williams, and N. L. Yoss; Clinical Chemistry, 19/8, pages 838-344 (1973). Such instruments can rapidly analyze body fluid samples labelled with a fluorescent material.
In the aforementioned article, a fluorescent polarization instrument is illustrated which includes a fluorescent sample irradiated by two beams of exciting light each linearly polarized, one vertically, the other horizontally. Alternate polarization sample excitation is provided by a sectored chopping mirror which alternately passes the vertically and horizontally polarized light to the sample. The exciting light is monochromatic corresponding to the peak of the absorption spectrum of the sample. The illuminated fluorescent sample becomes a secondary source of radiation, emitting light in a spectrum peaked at a longer wavelength than the exciting light. A vertical polarizer in the emission light path passes vertically polarized light to a photomultiplier tube for detecting the resulting emission light from the sample. The signal output of the photomultiplier tube then is analyzed to obtain the degree of polarization, P, which is determined by the expression: I(VV)-I(HV)/I(VV)+I(HV), where I(VV) is the measured intensity of the detected photomultiplier signal when vertically polarized light excites the sample and the vertical component of the emitted light is analyzed, and I(HV) is the detected photomultiplier signal when horizontally polarized light excites the sample and the vertical component of the emitted light is analyzed.
Known instruments of such type require relatively high wattage, intense light sources such as 200-250 watt mercury or xenon gas discharge lamps in order to obtain the desired emission radiation from the sample at a signal to noise level ratio sufficient for detection and amplification by a low-noise photomultiplier tube and associated electronics. Such high wattage, bright lamps also require substantial cooling in order to maintain the integrity of the optical system. It is thus desired to provide an improved optical system for fluorescence polarization instrument which can utilize lower wattage and less intense lamps and yet provide sensitivity which is equal to or better than prior art devices.